Oral transmission of human immunodeficiency virus (HIV) as a potential risk factor for HIV/AIDS spread is being intensively investigated, but the mechanisms of HIV interaction with oral mucosal epithelium in vivo are not well understood. Analysis of HIV infection in clinical specimens of oropharyngeal mucosal epithelium and saliva showed that HIV can be detected in both, indicating a key role of the oral cavity in HIV transmission and dissemination. Primary oral keratinocytes in vitro also can be infected by HIV-1, and they can transfer virus to lymphocytes. Our preliminary data show that HIV- 1 transcytosis can occur across polarized Detroit pharyngeal epithelial cells, indicating that oral HIV transmission may occur by transepithelial transcytosis through the epithelial barrier without infecting the epithelial cells. We also found that interepithelial Langerhans cells (LCs) in the HIV/AIDS-associated oral lesion called hairy leukoplakia are infected simultaneously with HIV and EBV, suggesting a critical role of LCs and HIV-EBV interactions in HIV pathogenesis in the oral cavity. Since suitable in vivo and in vitro oral mucosal epithelial model systems for evaluation of HIV infection are not available, our goal in this proposal is to establish an in vitro organ culture system from oral mucosal tissue and to use it to investigate HIV-1 infection. This system will also be used to study HIV and EBV interaction, since both viruses can replicate in oropharyngeal mucosal epithelium. The specific aims of the study are: (1) To establish an in vitro organ culture model derived from squamous oral tissue. (2) To investigate infection of HIV-1 in the organotropic oral mucosal epithelial cell culture. (3) To study the effect of EBV on HIV infection in Langerhans cells of the organotropic oral mucosal epithelial tissue model. The results of these studies will provide new and detailed information on the mechanisms of HIV infection of the oral mucosal epithelium and the role of HIV-EBV infection in oral interepithelial LCs in HIV pathogenesis.